Groundwater response to tidal fluctuations in a leaky confined coastal aquifer with a finite length

The study on the hydraulic properties of coastal aquifers has significant implications both in hydrological sciences and environmental engineering. Although many analytical solutions are available, most of them are based on the same basic assumption that assumes aquifers extend landward semi‐infinitely, which does not necessarily reflect the reality. In this study, the general solutions for a leaky confined coastal aquifer have been developed that consider both finitely landward constant‐head and no‐flow boundaries. The newly developed solutions were then used to examine theoretically the joint effects of leakage and aquifer length on hydraulic head fluctuations within the leaky confined aquifer, and the validity of using the simplified solution, which assumes the aquifer is semi‐infinite. The results illustrated that the use of the simplified solution may cause significant errors, depending on joint effects of leakage and aquifer length. A dimensionless characteristic parameter was then proposed as an index for judging the applicability of the simplified solution. In addition, practical application of the general solution for the constant‐head inland boundary was used to characterize the hydraulic properties of a leaky confined aquifer using the data collected from a field site at the Seine River estuary, France, and the versatility of the general solution was further justified.     

Magnetic Field Vector Retrieval With the Helioseismic and Magnetic Imager

We investigate the accuracy to which we can retrieve the solar photospheric magnetic field vector using the Helioseismic and Magnetic Imager (HMI) that will fly onboard of the Solar Dynamics Observatory by inverting simulated HMI profiles. The simulated profiles realistically take into account the effects of the photon noise, limited spectral resolution, instrumental polarization modulation, solar p modes, and temporal averaging. The accuracy of the determination of the magnetic field vector is studied by considering the different operational modes of the instrument.     

中国土地利用变化遥感研究的回顾与展望——基于陈述彭学术思想的引领

20世纪80年代以来中国社会经济快速发展带来的工业化、城市化正深刻影响着中国土地利用空间格局并影响到区域和国家生态与环境状况。在陈述彭先生指导下,1992年以来中国科学院建立起了完整的土地利用/覆盖变化遥感监测与数据分析技术路线,以及独特的分类体系和动态区划体系,奠定了中国LUCC信息平台的基础。本文在系统回顾陈述彭学术思想指导中国LUCC研究的基础上,面向国家需求与国际科技前沿梳理了我国LUCC研究的核心科学问题,并总结了中国科学院团队在最近20年LUCC研究取得的成果,包括土地利用/覆盖动态时空表征与分析模型、土地利用/覆盖变化过程及驱动机制、基于大数据和云计算的土地利用/覆盖变化探测方法、城市土地利用变化的区域气候/生态效应、气候变化与土地利用变化对农田生态系统的影响、林业活动的区域气候/生态效应,在此基础上对未来LUCC研究的前景进行了展望。     

On vertical dynamic stability and cross‐section optimization of closed‐ended hollow pile by considering soil compaction effects

This paper conducts a comprehensive study on the effects of expansion force after pile driving on the vertical vibration of the hollow pile. The initial radially inhomogeneous strain field of soil in disturbed soil region and dynamic shear modulus of remolded soil are constructed by applying the cylindrical cavity expansion method. The equation governing the incremental motion of the soil is consequently deduced on the basis of incremental deformations superposed on an underlying finite deformation. The longitudinal impedance of the top of the pile and the velocity response in frequency and time domains are also numerically studied. The relations between the expansion force after pile driving and the velocity response of the pile with different wall thickness are discussed accordingly. The results suggest that a pile has a better dynamical stability when the characteristics of the section are optimized and interacting force with soil medium gets smaller.     

Influences of upstream reservoir stratification and downstream tidal fluctuations on the summer thermal regime of a regulated coastal river

This study focused on the effects of upstream reservoir thermal dynamics and downstream tidal influences on temperatures in a 25-km reach of Alouette River (coastal British Columbia, Canada) below a control dam and upstream of its confluence with Pitt River. Temperature was monitored during summer 2013 using 25 sensors. Water was released from the reservoir through a low level outlet at approximately 2.7 m³ s⁻¹, except during late spring when a higher flow was released over the dam spillway. Temperature variations in the lowest section of Alouette River, and in the lower portion of a tributary, were distinct from those further upstream due to backwatering effects associated with a semi-diurnal tide, which can cause flow reversals in Pitt River. An internal seiche was identified in the reservoir during mid-summer that resulted in oscillating releases of warmer and cooler water with an amplitude of up to 6°C and a period of approximately 12 hr. Wavelet analysis and band-pass filtering indicated that the 12-hr signal declined in strength with downstream distance, but remained detectable about 15 km below the dam. In contrast, the 24-hr diel signal increased in strength with distance below the dam. Travel times computed via cross-correlation of the 12-hr signals with that at the low level outlet were within ±10% of those estimated from measured mean velocities. Lagrangian tracking of water parcels using the derived travel times indicated that the cooling effect of periodic releases of cold water during the seiching period persisted to the lower extent of the non-tidal reach. The tidally influenced locations experienced higher temperatures than those recorded in the non-tidal portion of Alouette River, although the relative roles of heating in the upstream tidal reach versus upstream advection of water associated with tide-driven flow reversals in Pitt River require further study.     

化学作用下高庙子膨润土屏障性能演化行为

深地质处置库运营过程中,受地下水化学成分、可能泄露的核素等近场化学条件影响,膨润土工程屏障性能可能发生衰减。围绕化学作用下膨润土屏障性能的演化行为,以我国北山处置库预选场地为工程背景,以内蒙古高庙子膨润土为研究对象,首先介绍了高庙子膨润土的基本物理性质及北山预选场地近场化学条件;在此基础上,详细总结了化学作用下高庙子膨润土水力、力学及阻滞等屏障性能演化行为相关研究成果。结果表明:化学作用对膨润土持水、渗透特性的影响可分别依据渗透吸力及双电层理论解释;化学作用下膨润土膨胀力的衰减与其水化膨胀机制有关,化-力耦合及化-水-力耦合作用下膨润土变形特性因渗透固结、化学软化效应而发生改变;膨润土的吸附与扩散特性受核素浓度、离子环境、pH值等因素影响。最后,提出化学作用下膨润土屏障性能演化研究应重点关注的方向。     

峨汉高速庙子坪隧道岩溶发育特征及工程效应分析

以峨汉(峨眉山市—雅安市汉源县)高速庙子坪隧道为研究对象,首先通过对隧址区地质调查、示踪试验及统计现场揭露的溶洞数量,厘清隧址区岩溶发育特征并分析其控制因素,再通过整理分析现场监测数据探究岩溶发育对工程的影响。结果表明:隧址区岩溶在多溶控因素的耦合作用下表现出显著的不均性、集中性、方向性、连通性的特征。其中岩层岩性、地形地貌、水文地质、地质构造主要使得岩溶发育具有不均性和集中性;水文地质与地形地貌主要控制着岩溶发育方向和岩溶是否连通;气候则更进一步促进岩溶发育。隧址区岩溶发育的工程影响主要表现为隧道稳定性影响和隧道涌水,其中岩溶规模及尺寸对隧道稳定性有一定影响,但影响范围相对有限;而涌水使得隧道长期积水,在雨季时甚至使得人员、机械等被淹或冲毁,对隧道安全、进度、经济等造成严重影响。研究结论可为峨汉高速沿线隧道及其他类似工程的设计、施工、岩溶灾害防治等提供参考。     

沙被的定义、类型及其生态效应

文章提出了沙被的概念和定义,即:沙物质在地表积聚形成的覆被。阐述了依据沙被所处的气候区与植被区、沙被形态、颜色、有无植被、位于表层还是下层等特征的沙被分类方式。同时,指出了沙被的水平结构和从沙被边缘到中心其形态变化、植被变化的规律,研究和探讨了沙被的生态效应、与植被、风的关系和沙被的动态变化特点,以及沙被生态系统的保护修复与开发利用的原则。     

重大水利工程对长江中下游干流河槽和岸线地质环境影响研究

本文主要采取历史水下地形和水位数据分析、干流河槽现场测量、室内测试和综合评价等方法对重大水利工程影响长江中下游干流河槽和岸线进行了分析和研究,取得如下新进展：（1）创新构建了一套多模态传感器系统,实现陆上和水下一体化水动力、沉积和地貌特征测量与数据采集。（2）调查研究发现,长江干流河槽冲刷强烈,岸线窝崩、条崩发育。（3）悬沙和床沙粗化,河床阻力下降,发育侵蚀型链珠状沙波,长江大桥主桥墩冲刷严重。（4）潮区界显著上移,潮区界变动河段地貌发生重要变化。在此基础上,研究认为应该加强长江中下游干流河槽、沿岸高陡岸坡、支流入汇干流河口、崩岸以及跨江大桥桥墩冲刷等调查、监测和成因机理分析。上述研究成果对长江岸滩防护和修复、航道整治、沿岸防洪、长江大桥桥墩维护等具有重要意义。     

Impacts of hegemony and shifts in dominance on marine capture fisheries

Catch data indicates that the world’s 25 largest marine capture fisheries have generally comprised some 40–50% of the total annual reported catch (1950–2012). From a game theory perspective, there is considerable diversity across these 25 fisheries, both in terms of the number of players and the management paradigms. Here, a dominance-oriented classification system is proposed, according to which fisheries are categorized into: (1) hegemonic systems with single-player dominance; (2) coupled systems with two-player dominance; (3) group systems with shared dominance; (4) systems with no dominant player. Among these categories, the fourth represents perhaps the greatest challenge to sustainable management, while also demonstrating the challenges of managing common pool marine ecosystem services in areas beyond national jurisdiction (ABNJ). The survey and analysis highlights how hegemonic conditions tend to preclude the establishment of cooperative agreements irrespective of the number of players involved in the fishery. Shifts in dominance away from hegemony, as demonstrated most recently in the case of the highly migratory Pacific Saury, can open the door to greater cooperation. Movement of fish stocks and displacement of fishing activities, due for example to climate change, have the capacity to cause major shifts in dominance and, in some cases, destabilize existing cooperative mechanisms.